Chapter 3. NFS and the User-Defined File System (UDFS)
A user-defined file system (UDFS) is a type of file system that you directly manage
through the end user interface. This contrasts with a system-defined file system
(SDFS), which AS/400 system code creates. QDLS, QSYS.LIB, and QOPT are all
examples of SDFSs.
The UDFS introduces a concept on AS/400 that allows you to create and manage
your own file systems on a particular user Auxiliary Storage Pool (ASP).An ASP is
a storage unit that is defined from the disk units or disk unit sub-systems that make
up auxiliary storage. ASPs provide a means for placing certain objects on specific
disk units to prevent the loss of data due to disk media failures on other disk units.
The concept of Block Special Files (*BLKSF objects) allows a user to view a UDFS
as a single entity whose contents become visible only after mounting the UDFS in
the local namespace. An unmounted UDFS appears as a single, opaque entity to
the user.Access to individual objects within a UDFS from the integrated file system
interface is permissible only when the UDFS is mounted.
UDFS support enables you to choose which ASP will contain the file system, as
well as manage file system attributes like case-sensitivity.You can export a
mounted UDFS to NFS clients so that these clients can also share the data that is
stored on your ASP.This chapter explains how to create and work with a UDFS so
that it can be used through NFS.

User File System Management

The UDFS provides new file management strategies to the user and includes
several new and changed CL commands specific to UDFSs.
For more information about the various UDFS CL commands and their associated
parameters and options, see
CL Reference,
SC41-4722.

Create a User-Defined File System

The Create User-Defined File System (CRTUDFS) command creates a file system
whose contents can be made visible to the rest of the integrated file system
namespace via the ADDMFS (Add Mounted File System) or MOUNT command.A
UDFS is represented by the object type *BLKSF,or block special file. Users can
create a UDFS in an ASP of their own choice and have the ability to specify
case-sensitivity.
Restrictions:
1. Youmust have *IOSYSCFG special authority to use this command.
© Copyright IBM Corp. 1997, 1999 15
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